The present invention is related to locomotive air brake apparatus and especially to such apparatus for cutting off the brake pipe charging function of the locomotive brake valve device in response to an emergency rate of brake pipe pressure reduction, as occurs for example due to a break-in-two between the normally coupled cars and/or locomotives of a railway train.
It is common practice to provide charging cut-off of the train brake pipe pressure in response to an emergency rate of reduction of brake pipe pressure in order to enhance the ability of the brake equipment to automatically produce an emergency brake application in response to such brake pipe pressure reduction. One such device employed to provide the rake pipe charging cut-off function is the A-1 Charging Cut-Off Pilot Valve employed in the standard 26-L Locomotive Brake Equipment shown in WABCO Instruction Pamphlet No. 5071-6. This valve, however, is somewhat intolerant to harsh environmental conditions and is thus limited in its location, in addition to being relatively expensive.
An alternative arrangement disclosed in the aforementioned Instruction Pamphlet discloses a pair of RELAYAIR type valves in a scheme functionally similar to the previous mentioned arrangement. Both of these schemes are designed to operate with a standard 26-C type brake valve, also shown in the mentioned Instruction Pamphlet, by supplying air to actuate the brake pipe cut-off valve.
In addition, WABCO Instruction Pamphlet No. 5071-24 shows another brake pipe charging cut-off arrangement in which a single, modified RELAYAIR valve designated SI-1 unit is arranged to pilot a valve in the 26-E type brake valve, in response to a reduction of brake pipe pressure at an emergency rate. This pilot valve, in turn, supplies actuating air to the brake pipe cut-off valve to cut off brake pipe charging. The SI-1 unit is more tolerant to environmental conditions than the counterpart A-1 Charging Cut-Off Pilot Valve and is also less expensive. This cost savings, however, is offset by the added cost of a special back cover to accommodate the pilot valve in the 26-E type brake valve, with which the SI-1 unit is employed.